One form of high-performance valve for applying cold or hot fluid product in dot or line form, involves electromagnetic actuation and comprises a piston which is disposed in a solenoid and which is in two parts. One of the parts of the piston is a piston member which is stationary in operation while the other part of the piston is a valve piston which bears against a valve seat under the effect of a biasing force and which is braced against the stationary piston and which in the closed condition of the valve closes off a valve opening. The valve has feed devices for the feed of the fluid product to be applied, and through-flow openings for the fluid product are provided in the region of the piston. The fluid product to be applied may be for example dye, ink, oil, adhesives, thermoplastic fluids, fusion adhesives and the like. A valve of that design configuration is to be found for example in DE 38 474 Al.
In that valve, the fluid product is supplied through a central passage which is disposed in the stationary piston and which opens into a central distribution chamber. The through-flow openings which are provided in the region of the valve piston are of such a configuration that they are formed on the one hand by a concentric bore which extends over a part of the longitudinal extent of the valve piston and which communicates with a recess, through a discharge flow bore, at the lower end of the concentric bore. That configuration involves repeated transverse deflections of the fluid flowing through the passage, and that prevents a smooth flow of fluid from taking place through the valve.
The valve piston in the above-discussed valve is relatively long and is guided separately above the valve seat. The valve piston is also of relatively large mass and is moved only by about a quarter in the coil body or former of the solenoid unit. The design configuration of the valve piston means that the cyclic performance of the valve is limited, on the one hand as a result of the large mass of the valve piston which has to be accelerated and decelerated again in each cycle of operation of the valve, and on the other hand because of the flow of fluid which acts on the piston and which is only very poorly distributed around the piston. Another disadvantage of that valve is that it can suffer from overheating, in particular when required to operate at high levels of cyclic performance. If the temperature of the valve exceeds a certain limit, that will give rise to problems and operational deficiencies.